In recent years, in a case where a desired digital communication device is set to be an object to be measured and a bit error rate in the object to be measured is measured, for example, an error rate measurement device as disclosed in Patent Document 1 to be described below has been used. Since this type of error rate measurement device measures to what extent the object to be measured can permit electrical stress, jitter proof strength measurement is performed in which an electrical stress signal having a known pattern is applied as a test signal from a pattern generator, and the test signal is looped back inside or outside the object to be measured, whereby the presence or absence of an error is measured with respect to, for example, the amount of test signal applied, through comparison with the test signal received by an error detector.
Incidentally, a USB is known as one of serial bus standards for connecting a peripheral equipment to an information equipment such as a computer. In negotiation when performing various measurements by using a USB device or a host as an object to be measured, a three-valued LFPS signal specified by a USB 3.0/3.1/3.2 standard is used. The three-valued LFPS signal is a burst signal (tBurst, tRepeat), as illustrated in FIG. 5, which is constituted by pulses having, for example, a period of 20 ns to 100 ns (tPeriod) and a duty ratio of 40% to 60%. Although not particularly shown in the drawing, a signal for determining an operation mode is defined in the USB 3.0/3.1/3.2 standard, inclusive of an LFPS transmission time.
In recent years, in an error rate measurement device, various measurements are executed by making a state diagram of a USB device or a host transition to a loop-back mode during negotiation and causing an error detector to receive an LFPS signal looped back from the USB device or the host along a frame, but a two-valued NRZ signal of a high level and a low level is regarded as a three-valued LFPS signal specified by a USB 3.0/3.1/3.2 standard and is used during the negotiation.